By Leanna Coy, FNP-BC
KEY TAKEAWAYS:
• FDA-approved blood tests are now available to aid in diagnosing Alzheimer’s disease.
• Currently, 11% of people age 65 and older have Alzheimer’s. That number is expected to double by 2050.
• A positive blood test result alone does not confirm an Alzheimer’s diagnosis.
Marva moved in with her youngest daughter’s family after her husband died. She lived in her own apartment in the home and helped care for her young grandchildren. For years, the living situation worked out well for everyone. Then the family began to notice subtle shifts with Marva – memory lapses, mood shifts. Testing found she had Alzheimer’s disease. When her care became too much for her daughter, she was moved to a care facility where her condition declined rapidly.
An estimated 7.4 million Americans currently live with Alzheimer’s dementia. This devastating disease slowly robs the afflicted person of their memories and themselves. Traditionally, research focused on treatment after symptoms appeared. Recently, the Food and Drug Administration (FDA) approved the first blood tests to aid in diagnosing the disease, giving new hope for an earlier diagnosis. These tests have the potential to diagnose before symptoms even appear – allowing treatment to begin sooner and slowing mental decline.
What is Alzheimer’s Disease
Alzheimer’s disease is a form of dementia. Dementia is a group of symptoms that regularly occur together – a loss of memory, problem-solving, trouble concentrating or expressing thoughts, confusion, poor judgment, and impulsive behaviors. There are many types of dementia, each of which is related to specific changes in the brain. Most people with dementia will have more than one type, with Alzheimer’s being the most common form, accounting for 60-80% of dementia cases.
Alzheimer’s affects a person’s memory, how they think, and their behavior. It is a progressive disease with mild memory loss in the early stages. Symptoms gradually worsen over years until they begin to disrupt someone’s daily tasks. Eventually, the person loses their ability to care for themselves. The average lifespan after an Alzheimer’s diagnosis is four to eight years, but other factors can extend the lifespan to 20 years. These factors include age at diagnosis, other health conditions, and how far the disease has progressed.
The majority of the people living with the disease are over age 65. About 11% of adults over age 65 live with Alzheimer’s dementia, with the figure climbing to 35.8% after age 85. Although the greatest risk factor for developing the disease is aging, Alzheimer’s is not a normal part of aging.
Changing Methods of Detection
When someone begins experiencing memory issues, there is no single test for determining the presence of dementia. Often, testing starts with a standard physical exam, blood tests, and cognitive (memory) tests to look for issues that could cause dementia-like symptoms. Conditions such as alcohol use, depression, or thyroid problems often trigger dementia-like symptoms that may be reversible with treatment.
Brain scans are commonly used for early detection when someone has memory problems. They help rule out other causes and help determine the type of brain changes present. The scan set a baseline to track changes over time. Because normal aging can cause some of the same changes, brain scans are not used alone in diagnosing Alzheimer’s.
The Alzheimer’s Blood Test
Last year, the FDA approved two blood tests to aid in diagnosing Alzheimer’s disease. The tests are less invasive and more affordable than brain scans. The blood tests look for specific proteins in the bloodstream. In Alzheimer’s disease, tau is a protein biomarker that builds up and forms amyloid plaques in the brain. High levels of tau protein in the blood are highly suggestive that Alzheimer’s is the cause of someone’s cognitive decline.
Traditionally, a positron emission tomography (PET) scan of the brain was used to find these plaques. The main drawbacks of a PET scan are the cost, which can run into thousands of dollars, and the radiation exposure to the patient. The blood test requires only a simple blood draw and can increase access to follow-up testing.
Neither the PET scan nor blood testing is done alone for the purpose of screening for Alzheimer’s disease. They are tools used to aid in diagnosing Alzheimer’s when someone exhibits signs and symptoms of the disease. This is because the plaques can occur with other diseases.
Right now, there are two blood tests that check for signs of Alzheimer’s.
Lumipulse is for the early detection of Alzheimer’s disease in people 50 and older who have signs and symptoms of the disease. This test is used only by specialists, such as gerontologists and neurologists, and looks for the Alzheimer’s protein.
Elecsys is the first blood test to rule out Alzheimer’s that is available in primary care offices. It is only for people 55 or older who present with signs and symptoms of cognitive decline.
These tests can rule out Alzheimer’s when amyloid buildup is not found, suggesting the provider should look for other causes of the dementia symptoms. A positive result alone does not independently diagnose Alzheimer’s with either test. Limitations include possible interference from other health conditions and the need for further diagnostic confirmation by healthcare professionals.
Tracking Shifts in Biomarkers
More recently, researchers tracking biomarkers over five years found that steep increases in biomarkers were tied to a measurable decline in cognitive impairment. In the study, 20% of participants who started with normal biomarker screening results later developed abnormal results. This was a small study of healthy individuals, but it shows that screening over time may provide a clearer picture of a person’s Alzheimer’s risk.
The drawback of blood tests is interference from other problems in the body. One major problem is abnormal kidney function, which makes the test unreliable for about 1/3 of older adults. This includes mild changes to kidney function. An estimated 34% of Americans over age 65 are living with chronic kidney disease, which is again why the blood test alone is not adequate for an Alzheimer’s diagnosis. Medication, obesity, and vascular conditions can also affect the blood test results.
Researchers found that obesity may mask the development of biomarkers. A higher body mass index appears to dilute levels of the biomarkers in the blood tests. But repeat blood tests over time showed large increases in Alzheimer’s-related proteins. Despite limitations, studies show that monitoring biomarkers over time may offer potential benefits.
Alzheimer’s disease can start 20 years or more before someone begins having detectable symptoms. The current blood tests are promising for early identification when symptoms appear, but are not intended for routine or curiosity screenings. The limited Medicare coverage for these tests and the potential for interference from other health issues mean the blood tests aren’t for everyone.
Cognitive decline due to Alzheimer’s means brain damage has already begun. The new blood tests offer a promising future of early detection, which could reduce the time between diagnosis and the start of treatment. If you have concerns about your risk for Alzheimer’s, consult with your healthcare provider so they can review your health history and begin screening if needed.
Resources:
Alzheimer’s Association – https://www.alz.org/abam
